This invention relates to an improved heat transfer conduit, and more particularly, to a heat transfer tube through which a vaporizable fluid is passed in heat exchange relation with a source of heat such as hot gases.
Most vapor generators include a plurality of heat transfer tubes through which a vaporizable fluid is passed. The tubes are usually subjected to a source of heat, such as hot gases in a furnace, and serve to transfer heat to the fluid passing therethrough. Water is one such vaporizable fluid used in these vapor generators. As the water is passed through the tubes, which are usually metallic, steam may form at the interface of the water and the internal surface of the tube. This formation of steam inhibits the transfer of heat from the tube to the water passing through the tube.
It has been known that internal grooving, or rifling, of tubes can improve the heat transfer between the fluid flowing through the tube and the tube itself. In some known grooving or rifling methods, grooves are cut into a tube wall, and tube wall material is removed as a consequence. In other known grooving methods, the tube is drawn over a groove forming plug such that the inside and outside tube diameters are reduced, with grooves being formed in the inside wall as the wall contacts the groove forming plug. In neither of these operations is tube internal wall material relocated so as to form a lip adjacent the grooves formed. The instant invention provides an improvement in an internally grooved tube that serves to promote mixing of fluid contained in heat transfer tubes so as to reduce or eliminate any vapor barrier that could be formed between the liquid and the tube surface and thereby improve heat transfer between the tube and the fluid.